<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport"
        content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Title</title>
</head>
<body>
<script>
  // let str = "123";
  // let str1 = new String("123");
  //
  // console.log(typeof str);
  // console.log(typeof str1);
  //
  // str.number = 1;
  // console.log(str.number)

  function Num() {
    // this.num = 20;
  }

  Num.prototype.num = 10;
  let num = new Num();
  console.log(num.num);
</script>
</body>
</html>
